In cellular mobile radio networks, the geographical area covered by the network is divided into smaller radio coverage areas, i.e. radio cells, each comprising at least one base station. In each cell, a certain number of frequency channels are assigned to the base station, and the frequency channels, in turn, may be time-division multiplexed into several traffic channels on the TDMA principle. Typically, the size and density of the radio cells as well as the number of frequency channels assigned to them are determined by the traffic capacity requirements in each particular area. The cellular mobile radio network may, however, comprise radio cells or larger areas in which the traffic capacity requirements may increase temporarily to a very high degree, e.g. at certain hours of the day. If the number of channels assigned to the radio cell is now determined on the basis of this instantaneous maximum capacity, the number of channels will be high, resulting in a higher number of radio equipments at the base station and therefore higher costs. Such an arrangement does not either enable efficient utilization of radio frequencies in the network. On the other hand, if the number of channels and the base station equipment are not dimensioned on the basis of the peak traffic in a service area, the number of rejected calls will be very high within that service area at peak hours.
In certain prior art networks, attempts have been made to alleviate the capacity problem by increasing transmitting powers in the network. In GB Patent Specification 1562963, the mobile radios are able to increase the coverage area (transmitting power) of their transmissions when adjacent base stations are overloaded in order to establish a connection to less loaded, more remote base stations. U.S. Patent Specification 4435840, in turn, teaches a cellular system in which the cell size of an overloaded base station is temporarily decreased by reducing its transmitting power while correspondingly increasing the transmitting power and the cell size of a neighbouring base station. Changes in transmitting powers may, however, cause interference elsewhere in the network and complicate the design of the network.